Reducing sewage sludge ash variability in the context of P-recovery by optimizing the storage management using Monte-Carlo simulations

Phosphorus (P) is a critical raw material and the EU largely depends on P-imports to cover its demand. This is increasing efforts to recover P from secondary P-sources such as municipal sewage sludge ashes (SSA) from mono-incineration. Usage of SSA for mineral fertilizer production requires compliance with certain quality standards regarding P-concentrations and trace element levels. This is particularly challenging in view of the variability in composition and amount of sewage sludge due to different technologies applied by the wastewater treatment plants (WWTP) and various catchment areas when sludge is jointly incinerated. By applying different sewage sludge treatment processes along the process chain, homogenization of the output quality of mono-incineration plants may be achieved. To investigate the effects of input variability and treatment processes on SSA composition a Monte-Carlo simulation approach was used. The simulations included probability distributions of sewage sludge composition data from 57 WWTP. Missing data were compensated by mean substitution to generate a complete set of input distributions. The resulting distributions of SSA nutrient and contaminant concentrations obtained by the simulation were compared.